I get this question from time to time. It really can be a challenge at times but there are some things that work for me. For instance, I have two fifth graders and a fourth grader. I am able to teach them some subjects like science and history together making my job easier. I am even able to include my second grader in some of those activities.
I try to use my children's strengths when schooling. One example is that my second grader is a little mother. She was born believing that she has the answers. Wink, wink. This personality can be a challenge sometimes and there are occasions where I have to remind her that only one mother is needed in our house. On the flip side that personality can also be a valuable asset. When I have a subject or activity that I need to do with the older kids I will send her with a Science reader and her little brother to the family room. Here she will "teach" him from her reader. They do the activities together, she learns, gets her reading done and our youngest is read to. It's win-win. Sometimes getting it all done includes delegation. I am still the primary teacher but I try to use the strengths of my kids to all of our advantage.